Lateral electrochemical etching of III-nitride materials for microfabrication

Abstract

Conductivity-selective lateral etching of III-nitride materials is described. Methods and structures for making vertical cavity surface emitting lasers with distributed Bragg reflectors via electrochemical etching are described. Layer-selective, lateral electrochemical etching of multi-layer stacks is employed to form semiconductor/air DBR structures adjacent active multiple quantum well regions of the lasers. The electrochemical etching techniques are suitable for high-volume production of lasers and other III-nitride devices, such as lasers, HEMT transistors, power transistors, MEMs structures, and LEDs.

What is claimed is: 
     
       1. A method for laterally etching III-nitride material, the method comprising:
 depositing a first layer of III-nitride material having a first n-type conductivity on a substrate; 
 depositing a second layer of material over the first layer; 
 forming a via in the second layer to expose a surface area of the first layer; 
 electrochemically and laterally etching the first layer using a hydrofluoric-based etchant to selectively remove at least a portion of the first layer, wherein the removed portion of the first layer extends under the second layer and wherein the etching does not require illumination. 
 
     
     
       2. The method of  claim 1 , wherein the hydrofluoric-based etchant is non-aqueous. 
     
     
       3. The method of  claim 1 , wherein the hydrofluoric-based etchant comprises ethanol. 
     
     
       4. The method of  claim 3 , wherein the hydrofluoric-based etchant further comprises glycerol. 
     
     
       5. The method of  claim 1 , wherein the first layer has an n-type dopant concentration greater than 10 17  cm −3 . 
     
     
       6. The method of  claim 1 , wherein the first layer and second layer comprise GaN. 
     
     
       7. The method of  claim 1 , wherein the second layer comprises a III-nitride material of a different conductivity than the first layer. 
     
     
       8. The method of  claim 1 , further comprising laterally etching the at least a portion of the first layer for a lateral distance of more than approximately 5 microns. 
     
     
       9. The method of  claim 1 , further comprising:
 depositing a conductive ground plane proximal to the first layer; and 
 forming the via to extend to the conductive ground plane. 
 
     
     
       10. The method of  claim 9 , wherein the conductive ground plane extends laterally across a region of the first layer that is etched. 
     
     
       11. The method of  claim 1 , further comprising depositing a multi-layer stack of the first layers and the second layers, wherein the first layers and second layers alternate in the multi-layer stack. 
     
     
       12. The method of  claim 11 , wherein the via is formed through the multi-layer stack to expose side-wall surface areas of the first layers. 
     
     
       13. The method of  claim 12 , wherein the electrochemical etching removes portions of the first layers to form a region having at least two second layers separated by a layer of air. 
     
     
       14. The method of  claim 12 , wherein the electrochemical etching removes portions of the first layers to form a region having at least two second layers having layers of air on opposing sides of the second layers. 
     
     
       15. The method of  claim 14 , wherein the etched multi-layer stack comprises a DBR structure. 
     
     
       16. The method of  claim 14 , wherein the etched multi-layer stack comprises a DBR structure for a vertical cavity surface emitting layer. 
     
     
       17. The method of  claim 14 , wherein a number of second layers having layers of air on opposing sides of the second layers is four. 
     
     
       18. The method of  claim 14 , further comprising depositing a MQW structure adjacent the multi-layer stack. 
     
     
       19. The method of  claim 18 , further comprising depositing a dielectric DBR structure or a metallic film adjacent the MQW structure. 
     
     
       20. A method for etching III-nitride material, the method comprising:
 depositing a first layer of III-nitride material having a first n-type conductivity on a substrate; 
 depositing a second layer of material adjacent the first layer; 
 electrochemically and laterally etching the first layer using a hydrofluoric-based etchant to selectively remove at least a portion of the first layer that extends along the second layer without substantial removal of the second layer, wherein the etching does not require illumination. 
 
     
     
       21. The method of  claim 20 , wherein the first or second layer comprises a layer of an LED device. 
     
     
       22. The method of  claim 21 , wherein the LED device is a microcavity LED or a resonant cavity LED. 
     
     
       23. The method of  claim 20 , wherein the hydrofluoric-based etchant contains ethanol. 
     
     
       24. The method of  claim 23 , wherein the hydrofluoric acid before dilution with ethanol is approximately 50% volume in water. 
     
     
       25. A method for forming a distributed Bragg reflector (DBR) laser comprising III-nitride material, the method comprising:
 depositing a first multi-layer structure on a substrate, the first multi-layer structure comprising first and second layers, wherein the first layers have a conductivity different than that of the second layers; 
 depositing a multiple quantum well (MQW) active structure adjacent the first multi-layer structure; 
 forming vias into the first multi-layer structure so as to provide access for an etchant to the second layers; 
 laterally and electrochemically etching the second layers with a hydrofluoric-based etchant so as to selectively remove at least a portion of the second layers and form a DBR structure adjacent the MQW region, wherein the etching does not require illumination and wherein the DBR structure comprises at least two first layers separated by one or more layers of air. 
 
     
     
       26. The method of  claim 25 , wherein the etching comprises subjecting the first multi-layer structure to an etchant comprising hydrofluoric acid, ethanol, and glycerol. 
     
     
       27. The method of  claim 26 , wherein the etching comprises subjecting the first multi-layer structure and etchant to an electric bias between approximately 5 volts and approximately 60 volts, and wherein an n-type dopant concentration of the second layers is between approximately 10 17  cm −3  and approximately 10 20  cm −3 . 
     
     
       28. The method of  claim 27 , wherein subjecting the first multi-layer structure to an electric field comprises applying a potential difference between the etchant and the substrate that affects electropolishing or complete removal of the second layer material. 
     
     
       29. The method of  claim 25 , wherein the first layers and second layers comprise GaN. 
     
     
       30. The method of  claim 29 , wherein the second layers comprise n-type conductivity material having a dopant concentration between approximately 3×10 18  cm −3  and approximately 5×10 19  cm −3 . 
     
     
       31. The method of  claim 25 , wherein the thicknesses of the first layers are substantially the same. 
     
     
       32. The method of  claim 25 , wherein the thicknesses of the first layers correspond to approximately one-quarter of a selected emission wavelength for the laser. 
     
     
       33. The method of  claim 25 , wherein the removed portions of the second layers and remaining first layers form a structure having periodic contrast of optical refractive index. 
     
     
       34. The method of  claim 1 , further comprising applying a bias of between approximately 5 volts and approximately 60 volts, wherein a dopant concentration of the first layer is between approximately 10 17  cm −3  and approximately 10 20  cm −3 . 
     
     
       35. The method of  claim 1 , further comprising applying a bias of between approximately 10 volts and approximately 30 volts, wherein a dopant concentration of the first layer is between approximately 3×10 18  cm −3  and approximately 5×10 19  cm −3 .